linux-kernel - Re: [PATCH v11 13/16] KVM: x86/vmx: Clear Arch LBREn bit before inject #DB to guest

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Date:   Fri, 6 May 2022 11:08:13 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, pbonzini@...hat.com,
        jmattson@...gle.com, seanjc@...gle.com, like.xu.linux@...il.com,
        vkuznets@...hat.com, wei.w.wang@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 13/16] KVM: x86/vmx: Clear Arch LBREn bit before
 inject #DB to guest



On 5/5/2022 11:33 PM, Yang Weijiang wrote:
> On a debug breakpoint event (#DB), IA32_LBR_CTL.LBREn is cleared.
> So need to clear the bit manually before inject #DB.
> 
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>

Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>

> ---
>   arch/x86/kvm/vmx/vmx.c | 27 +++++++++++++++++++++++++++
>   1 file changed, 27 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index e6384ef1d115..6d6ee9cf82f5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1605,6 +1605,27 @@ static void vmx_clear_hlt(struct kvm_vcpu *vcpu)
>   		vmcs_write32(GUEST_ACTIVITY_STATE, GUEST_ACTIVITY_ACTIVE);
>   }
>   
> +static void flip_arch_lbr_ctl(struct kvm_vcpu *vcpu, bool on)
> +{
> +	struct lbr_desc *lbr_desc = vcpu_to_lbr_desc(vcpu);
> +	struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);
> +
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR) &&
> +	    test_bit(INTEL_PMC_IDX_FIXED_VLBR, pmu->pmc_in_use) &&
> +	    lbr_desc->event) {
> +		u64 old = vmcs_read64(GUEST_IA32_LBR_CTL);
> +		u64 new;
> +
> +		if (on)
> +			new = old | ARCH_LBR_CTL_LBREN;
> +		else
> +			new = old & ~ARCH_LBR_CTL_LBREN;
> +
> +		if (old != new)
> +			vmcs_write64(GUEST_IA32_LBR_CTL, new);
> +	}
> +}
> +
>   static void vmx_queue_exception(struct kvm_vcpu *vcpu)
>   {
>   	struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -1640,6 +1661,9 @@ static void vmx_queue_exception(struct kvm_vcpu *vcpu)
>   	vmcs_write32(VM_ENTRY_INTR_INFO_FIELD, intr_info);
>   
>   	vmx_clear_hlt(vcpu);
> +
> +	if (nr == DB_VECTOR)
> +		flip_arch_lbr_ctl(vcpu, false);
>   }
>   
>   static void vmx_setup_uret_msr(struct vcpu_vmx *vmx, unsigned int msr,
> @@ -4645,6 +4669,9 @@ static void vmx_inject_nmi(struct kvm_vcpu *vcpu)
>   			INTR_TYPE_NMI_INTR | INTR_INFO_VALID_MASK | NMI_VECTOR);
>   
>   	vmx_clear_hlt(vcpu);
> +
> +	if (vcpu->arch.exception.nr == DB_VECTOR)
> +		flip_arch_lbr_ctl(vcpu, false);
>   }
>   
>   bool vmx_get_nmi_mask(struct kvm_vcpu *vcpu)